CR系统空间频率处理对影像质量影响的探讨  

The exploring of the effect of spatial frequency processing upon imaging quality in CR system

作　　者：宋少娟[1] 官秋清[1] 张建梅[1] 张梦龙[1] 

机构地区：[1]山东省医学影像学研究所,山东济南250021

出　　处：《医学影像学杂志》2003年第7期506-509,共4页Journal of Medical Imaging

摘　　要：目的 :研究变化计算机X线摄影系统后处理中的空间频率参数 :频率等级和增强强度对输出影像噪声特性总的威纳频谱的影响。方法 :利用常规X线机对成像板曝光 ,固定其它后处理参数 ,仅变化RN、RE ,获取总的WS抽样照片 ,用显微密度计扫描 ,通过快速付立叶变换计算总的WS。结果 :( 1)在主扫描方向上总WS值的高频区 (ω =2 .5Lp/mm左右 )出现峰值 ;( 2 )当空间频率为 1.0Lp/mm时 ,主扫描方向上RN =9的总WS值为 4 .0 1× 10 -6mm2 ,是RN =5的WS值的0 .79倍 ,是RN =0的WS值的 0 .4 2倍 ;( 3)当空间频率为 1.0Lp/mm时 ,主扫描方向上RE =3的总的WS值为 5 .5 8× 10 -6mm2 ,是RE =1.0的WS值的 1.2 2倍 ,是RE =0 .3的WS值的 1.5 4倍。结论 :随着RN的增加 ,WS值变小 ,噪声下降 ;随着RE的增加 ,WS值变大 ,噪声相应增加。噪声的增加会淹没更多的影像信息 。Objective:To compare the noise of computed radiographic imaging under different frequency rank (RN) and degree of enhancement (RE) by means of studying the Wiener spectrum (WS) of them.Methods:With the conventional X ray unit an image plate were exposed. CR films were obtained with different spatial frequency processing and fixed gradation processing. WS values were calculated on the 100 thousand data obtained by scanning on micro densimeter for every film processed as discrete signal by using fast Fourier transformation (FFT).Results:WS values get to the peak at about ω=2.5Lp/mm. when the spatial frequency was 1.0Lp/mm, on subscan direction,the WS value at RN=9 was 4.01×10 -6 mm 2, which was 0.79 times of CR film's at RN=5, and 0.42 times of CR film's at RN=0; the WS value at RE=3 was 5.58×10 -6 mm 2, which was 1.22 times of CR film's at RE=1.0, and 1.54 times of CR film's at RE=0.3.Conclusion:In spatial frequency processing of CR, general WS decreased with increasing of RN, increased with increasing of RE. Some information can be submerged by noise, so the effect of RN and RE should not be neglected.

关 键 词：计算机X线摄影系统 噪声频率特性 影像后处理 

分 类 号：R814.3[医药卫生—影像医学与核医学]